Determining heating and cooling annual and peak loads

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Hi,

I am looking to determine building heating and cooling loads to size geothermal systems.

What is the most valid way to determine these loads? 1. Use "Ideal Air Loads", and then manipulating the loads with the cop and eer ratings of the ground-source-heat-pumps? 2. Use conventional HVAC, and then manipulating the loads with the cop and eer ratings of the ground-source-heat-pumps? 3. Attempt to simulate a ground source heat pump system.